Green Inhibitors to Reduce the Corrosion Damage

*Said Abbout*

#### **Abstract**

Over the last years, corrosion phenomenon is an important economical and lives lost, which calls in the last decades researches on its final resolution by various techniques. Through this book chapter, we present one of the most used methods to protect the metals: the corrosion inhibitor. We have presented the classification (liquid and gas phase), action mode (adsorption, barrier, reinforcing of the oxide layer, passivation, and formed insoluble complex), the application fields (water treatment, petroleum industry), and some particular inhibitors. In addition, we present a case study using a green corrosion inhibitor (GCI) prepared from the oil of *Ceratonia siliqua* L. seeds.

**Keywords:** corrosion inhibitor, volatile corrosion inhibitors, *Ceratonia siliqua* L., polarization and impedance measurements

#### **1. Introduction**

Corrosion is an unstoppable phenomenon, in order to avoid or reduce the corrosion of metallic materials; the corrosion inhibitor is one of the most effective and flexible means of corrosion prevention and mitigation [1].

#### **2. Generalities about the corrosion inhibitors**

#### **2.1 Definition and functions necessary in the corrosion inhibitor**

According to ISO 8044, the corrosion inhibitor is a chemical substance added to the corrosion system at a concentration chosen for its effectiveness; this causes a decrease in the corrosion rate of the metal without significantly modifying the concentration of any corrosive agent contained in the aggressive medium [2]. In addition, this role can be assured by other ways such as modification of the pH and incorporation of some metals like zinc in the chemical composition of the materials. In fact, such a definition cannot be perfect; however, it avoids to consider inhibitors as additives.

From this definition, a corrosion inhibitor must therefore verify some fundamental properties:

• Decreasing the corrosion rate of the metal while retaining the physicochemical characteristics of the latter


#### **2.2 Utilization conditions**

A corrosion inhibitor can be used as method of protection:


#### **3. Classification of the corrosion inhibitors**

Various authors have classified the corrosion inhibitors differently. Some authors prefer to group the inhibitors by their chemical functionality (organic or inorganic), others by their electrochemical reaction. **Figure 1** presents the classification of the corrosion inhibitors.

**25**

**Figure 3.**

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

The corrosion inhibitors can be classified in the liquid phase as a cathodic,

*Cathodic inhibitors* either slow the cathodic reaction itself or selectively precipitate on cathodic areas to increase the cathodic surface and limit the diffusion of aggressive species to these areas, which means a shift of the corrosion potential to a more negative potential (more than 85 mV) and a decrease in the cathodic current density. Cathodic inhibitors can provide inhibition by two different mechanisms: as cathodic poisons and as cathodic precipitates. Some cathodic inhibitors, such as arsenic and antimony compounds, work by making the recombination and discharge of hydrogen more difficult. Other cathodic inhibitors, such as calcium ions, zinc ions, or magnesium ions, may be precipitated as oxides to form a protective layer on the metal. Oxygen scavengers help to inhibit corrosion by preventing the cathodic depolarization caused by oxygen. The most commonly used oxygen scavenger at ambient temperature is probably sodium sulfite

*Anodic* (or passivating) *inhibitors* cause a large anodic shift of the corrosion potential to a more positive potential (more than 85 mV), forcing the metallic surface into the passivation range (slow the anodic reaction). There are two types of passivating inhibitors: oxidizing anions, such as chromate and nitrate, which can passivate steel in the absence of oxygen and the nonoxidizing ions, such as phosphate, tungstate, and molybdate, which require the presence of oxygen to passivate

Anodic inhibitors can actually cause pitting and accelerate corrosion when concentrations fall below minimum limits. This kind of problem is not encountered

**3.1 Liquid phase**

anodic, or mixed.

(Na2SO3) [6] (**Figure 2**).

in the case of cathodic inhibitors (**Figure 3**).

steel [7].

**Figure 2.**

*Effect of addition of the cathodic inhibitor.*

*Effect of addition of the anodic inhibitor.*

**Figure 1.** *Corrosion inhibitor classification.*

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

#### **3.1 Liquid phase**

*Corrosion*

certain biocides

pro-tection

**2.2 Utilization conditions**

corrosion [3].

of the corrosion inhibitors.

• Stable in the temperature range used

• Inexpensive compared to the savings it allows to achieve

A corrosion inhibitor can be used as method of protection:

of the inhibitor over the time being is easier to carry out.

in the case of the surface coating [5].

**3. Classification of the corrosion inhibitors**

• Effective at low concentrations

• Stable in the presence of other constituents, in particular with respect to

• Compatible with the current standards of nontoxicity and environmental

• As a *permanent protection*, the inhibitor allows the use of metallic materials (non-alloyed ferrous example) under satisfactory conditions of resistance to

• As a *temporary protection* during a period when the piece or installation is particularly susceptible to corrosion (storage, stripping, cleaning) [4]. In this case, the control of the system is a priori simpler, and the prediction of the behavior

• As a *supplementary protection* to improve the resistance against the corrosion,

Various authors have classified the corrosion inhibitors differently. Some authors

prefer to group the inhibitors by their chemical functionality (organic or inorganic), others by their electrochemical reaction. **Figure 1** presents the classification

**24**

**Figure 1.**

*Corrosion inhibitor classification.*

The corrosion inhibitors can be classified in the liquid phase as a cathodic, anodic, or mixed.

*Cathodic inhibitors* either slow the cathodic reaction itself or selectively precipitate on cathodic areas to increase the cathodic surface and limit the diffusion of aggressive species to these areas, which means a shift of the corrosion potential to a more negative potential (more than 85 mV) and a decrease in the cathodic current density. Cathodic inhibitors can provide inhibition by two different mechanisms: as cathodic poisons and as cathodic precipitates. Some cathodic inhibitors, such as arsenic and antimony compounds, work by making the recombination and discharge of hydrogen more difficult. Other cathodic inhibitors, such as calcium ions, zinc ions, or magnesium ions, may be precipitated as oxides to form a protective layer on the metal. Oxygen scavengers help to inhibit corrosion by preventing the cathodic depolarization caused by oxygen. The most commonly used oxygen scavenger at ambient temperature is probably sodium sulfite (Na2SO3) [6] (**Figure 2**).

*Anodic* (or passivating) *inhibitors* cause a large anodic shift of the corrosion potential to a more positive potential (more than 85 mV), forcing the metallic surface into the passivation range (slow the anodic reaction). There are two types of passivating inhibitors: oxidizing anions, such as chromate and nitrate, which can passivate steel in the absence of oxygen and the nonoxidizing ions, such as phosphate, tungstate, and molybdate, which require the presence of oxygen to passivate steel [7].

Anodic inhibitors can actually cause pitting and accelerate corrosion when concentrations fall below minimum limits. This kind of problem is not encountered in the case of cathodic inhibitors (**Figure 3**).

**Figure 2.** *Effect of addition of the cathodic inhibitor.*

**Figure 3.** *Effect of addition of the anodic inhibitor.*

**Figure 4.** *Effect of addition of the mixed inhibitor.*

*Mixed inhibitors* can decrease the cathodic and anodic reaction rates at the same time because they affect the oxidation and reduction reaction, with little change in the corrosion potential (less than 85 mV around the corrosion potential) [6] (**Figure 4**).

#### *3.1.1 Action mode of the corrosion inhibitors in liquid phase*

Each type of inhibitor is characterized by its action mode: adsorption, barrier, reinforcing of the oxide layer, passivation, and formed insoluble complex.

In the case of the interposition of a barrier between the metal and the corrosive medium, which is essential in acidic backgrounds, the role of adsorption of the compounds on the surface is essential.

The reinforcement of a pre-existing barrier, in general the oxide or hydroxide layer formed naturally in a neutral or alkaline medium, may consist of an extension of the oxide to the surface or of the precipitation of salts with weak places of the oxide, these salts being corrosive agents.

The formation of the barrier by interaction between the inhibitor and one or more species of the corrosive medium is a type of mechanism which is also specific for neutral or alkaline media.

Obviously, taking into these general notions, the mechanism of action of an inhibitor can be considered under two aspects: a mechanistic aspect (intervention in the fundamental corrosion processes) and a morphological aspect (intervention of the inhibitory molecule in the interfacial structure). It is also clear that the mechanism of action will differentiate strongly depending on the pH characteristics of the medium.

#### **3.2 Gas phase: volatile corrosion inhibitors**

Volatile corrosion inhibitor is referred to as gas molecules used as a corrosion inhibitor; they are intended for the temporary protection of metallic materials placed in the atmosphere, essentially in storage or transport condition. Their use is made either in the form of wrapping papers impregnated with product or in the form of powder or by spraying with a solution (volatile solvent) [8] (**Figure 5**).

Vapor phase inhibitors (VPI) or volatile corrosion inhibitors (VCI) are low nitrogen base salts (cyclohexylamine, dicyclohexylamine, guanidine), and weak acids (nitrous acid, carbonic acid, benzoic acid). The organic part ensures volatility and a certain protective power, and the inorganic part adjusts the volatility, which must correspond to vapor pressures between 10<sup>−</sup><sup>4</sup> and 10<sup>−</sup><sup>2</sup> mmHg at room temperature, and ensures the supply of groups of protectors (Ph-COO▬…).

**27**

pigment.

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

The inhibitor molecules acts by different ways; they are transported or dissoci-

• Effect on electrochemical processes, essentially on the anodic process:

The adsorption is more of a chemical type, and the molecule is difficult to remove afterwards. Despite this, the protective action is only maintained if the source of the inhibitor is itself maintained in the immediate environment of the

The molecule inhibitors have three areas of application which are in particular important for the use of these products: the petroleum industry, water treatment, and pickling/cleaning of metals. Other applications exist for inhibitors, which involve then more specific formulations, which will be described in the following.

The incorporation of a pigment having inhibitory properties in the coating primer provides most of the corrosion resistance provided by the coating. There are two types of pigments: the active inhibitor pigment and the inactive inhibitor

The *active inhibitor pigments*, partially soluble in water, exist on the surface metal

ated on the metal surface to ensure an excellent protection by:

• Adsorption leading to hydrophobization of the surface

These are essentially the inhibitors added to the paints.

under the coating, providing active protection of the metal [9].

blocking of sites or passivation

• pH effect

*Volatile corrosion inhibitor mechanism.*

**Figure 5.**

metal surface.

**4. Particular inhibitor**

**4.1 Inhibitors for coating**

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

*Corrosion*

(**Figure 4**).

**Figure 4.**

*Mixed inhibitors* can decrease the cathodic and anodic reaction rates at the same time because they affect the oxidation and reduction reaction, with little change in the corrosion potential (less than 85 mV around the corrosion potential) [6]

Each type of inhibitor is characterized by its action mode: adsorption, barrier,

In the case of the interposition of a barrier between the metal and the corrosive medium, which is essential in acidic backgrounds, the role of adsorption of the

The reinforcement of a pre-existing barrier, in general the oxide or hydroxide layer formed naturally in a neutral or alkaline medium, may consist of an extension of the oxide to the surface or of the precipitation of salts with weak places of the

The formation of the barrier by interaction between the inhibitor and one or more species of the corrosive medium is a type of mechanism which is also specific

Obviously, taking into these general notions, the mechanism of action of an inhibitor can be considered under two aspects: a mechanistic aspect (intervention in the fundamental corrosion processes) and a morphological aspect (intervention of the inhibitory molecule in the interfacial structure). It is also clear that the mechanism of action will differentiate strongly depending on the pH characteristics

Volatile corrosion inhibitor is referred to as gas molecules used as a corrosion inhibitor; they are intended for the temporary protection of metallic materials placed in the atmosphere, essentially in storage or transport condition. Their use is made either in the form of wrapping papers impregnated with product or in the form of powder or by spraying with a solution (volatile solvent) [8]

Vapor phase inhibitors (VPI) or volatile corrosion inhibitors (VCI) are low nitrogen base salts (cyclohexylamine, dicyclohexylamine, guanidine), and weak acids (nitrous acid, carbonic acid, benzoic acid). The organic part ensures volatility and a certain protective power, and the inorganic part adjusts

mmHg at room temperature, and ensures the supply of groups of protectors

and

the volatility, which must correspond to vapor pressures between 10<sup>−</sup><sup>4</sup>

reinforcing of the oxide layer, passivation, and formed insoluble complex.

*3.1.1 Action mode of the corrosion inhibitors in liquid phase*

compounds on the surface is essential.

*Effect of addition of the mixed inhibitor.*

oxide, these salts being corrosive agents.

**3.2 Gas phase: volatile corrosion inhibitors**

for neutral or alkaline media.

of the medium.

(**Figure 5**).

(Ph-COO▬…).

**26**

10<sup>−</sup><sup>2</sup>

**Figure 5.** *Volatile corrosion inhibitor mechanism.*

The inhibitor molecules acts by different ways; they are transported or dissociated on the metal surface to ensure an excellent protection by:


The adsorption is more of a chemical type, and the molecule is difficult to remove afterwards. Despite this, the protective action is only maintained if the source of the inhibitor is itself maintained in the immediate environment of the metal surface.

#### **4. Particular inhibitor**

The molecule inhibitors have three areas of application which are in particular important for the use of these products: the petroleum industry, water treatment, and pickling/cleaning of metals. Other applications exist for inhibitors, which involve then more specific formulations, which will be described in the following.

#### **4.1 Inhibitors for coating**

These are essentially the inhibitors added to the paints.

The incorporation of a pigment having inhibitory properties in the coating primer provides most of the corrosion resistance provided by the coating. There are two types of pigments: the active inhibitor pigment and the inactive inhibitor pigment.

The *active inhibitor pigments*, partially soluble in water, exist on the surface metal under the coating, providing active protection of the metal [9].

#### *Corrosion*

At the same time, it helps maintain an optimal ratio between the pigment volume concentration and the critical pigment volume concentration that means the film is not too compact to avoid blistering nor too loose to prevent the penetration of aggressive ions (Cl<sup>−</sup>).

	- Zinc-based formulations include:
	- Zinc powder, which provides cathodic protection of the steel coated, provided that the dry extract is greater than 92% of the mass paint.
	- Zinc chromate, used because of its solubility in water; very effective in paints on aluminum, as well as strontium chromate.
	- Lead-based formulations include:
	- Lead powder, whose mode of action is complex and passing probably by modifying the pH of the aqueous medium on contact paint (alkalization) and metal and reverse polarity between iron and lead, explaining cathodic protection of the ferrous material.
	- Lead oxide Pb3O4, many mechanisms of action are proposed: formation of mixed protective layers of PbO oxide corrosion products, formation of soaps with constituents of paint, etc.

The *inactive inhibitor pigments* are essentially iron oxides, natural or synthetic, whose role is only to adjust the pigment volume concentration around the critical concentration.

#### **5. Inhibitors for industrial section**

Although their use could theoretically be envisaged in most cases of corrosion (with, as main limitations, too large volume of the corrosive medium or the possible impossibility of incorporating additives therein), inhibitors have several traditional application fields [10]:


**29**

**Table 1.**

*metals and alloys.*

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

**6. Green corrosion inhibitors (GCI)**

same time.

alloys (**Table 1**).

C-steel, Ni, Zn

GCI is the molecule extract from plants; it has a double effect because it has a good ability to protect the metals and no negative effect on the environment at the

**Metal Inhibitor source Active ingredient References** Steel Tamarind [11] Steel Tea leaves [12] Steel Eucalyptus oil Monomtrene 1,8-cineole [13]

> napthoquinone resin and tannin, coumarine, Gallic, acid, and sterols)

volatile monoterpenes, canaric and related triterpene acids, reducing and

Unsaturated fatty acids and biflavnone

Molecular protonated organic species in the extract. Ascorbic acid, amino acids, flavonoids, Pigments and

Catechin [20]

Polysaccharide (mucilage and pectin) [21]

S-(1-propenyl) L-cysteine sulfoxide, and S-2-carboxypropyl glutathione

nonreducing sugars

[14]

[15]

[16]

[19]

[23]

[24]

Lawsonia extract (henna) Lawsone (2-hydroxy-1,4-

Steel Aloe leaves [17] Steel Mango/orange peels [18]

Zn Metal chelates of citric acid [22] Zn Onion juice S-containing acids (glutamyl peptides)

Sn Black radish [25]

*Green inhibitors used for corrosion inhibition of steel, steel alloys, aluminum, aluminum alloys, and other* 

carotene

Mild steel Gum exudate Hexuronic acid, neutral sugar residues,

Mild steel Garcinia kola seed Primary and secondary amines

Steel Hibiscus sabdariffa (Calyx

10–50%

Al Opuntia (modified stems cladodes)

Sn Natural honey (acacia chestnut)

Al-Mg alloy Aqueous extract of

extract) in 1 M H2SO4 and 2 M HCl solutions, stock

*Rosmarinus officinalis* neutral phenol subfraction of the aqueous extract

In the last few years, the researcher community had oriented to inhibitors extracted from plants such as essential and vegetable oil, flavonoids, coumarins, steroids, terpenoids, and condensed tannins. These substances are excellent inhibitors because they contain heteroatoms such as an N, O, P, and S. The free electrons on the heteroatoms form bonds with the electrons on the metal surface. Some atoms in water ionize to release a proton; thus, the now negatively charged heteroatom helps to free an electron on the heteroatom and forms a stronger bond with the metallic electrons. These properties confer them good inhibition properties. The following table summarized some green inhibitors used for corrosion inhibition of steels, steel alloys, aluminums, aluminum alloys, and other metals and

• Paint industry on metals where the inhibitors are additives ensuring the anticorrosion protection of metals.

*Corrosion*

of aggressive ions (Cl<sup>−</sup>).

• Main inhibitors used

○ Zinc-based formulations include:

○ Lead-based formulations include:

protection of the ferrous material.

with constituents of paint, etc.

**5. Inhibitors for industrial section**

safeguarding of installations.

anticorrosion protection of metals.

concentration.

application fields [10]:

At the same time, it helps maintain an optimal ratio between the pigment volume concentration and the critical pigment volume concentration that means the film is not too compact to avoid blistering nor too loose to prevent the penetration

○ Zinc powder, which provides cathodic protection of the steel coated, pro-

○ Zinc chromate, used because of its solubility in water; very effective in

○ Lead powder, whose mode of action is complex and passing probably by modifying the pH of the aqueous medium on contact paint (alkalization) and metal and reverse polarity between iron and lead, explaining cathodic

○ Lead oxide Pb3O4, many mechanisms of action are proposed: formation of mixed protective layers of PbO oxide corrosion products, formation of soaps

The *inactive inhibitor pigments* are essentially iron oxides, natural or synthetic, whose role is only to adjust the pigment volume concentration around the critical

Although their use could theoretically be envisaged in most cases of corrosion (with, as main limitations, too large volume of the corrosive medium or the possible impossibility of incorporating additives therein), inhibitors have several traditional

• Water treatment (sanitary water, industrial process water, boiler water, etc.).

• Petroleum industry: drilling, extraction, refining, storage, and transport; at all stages of this industry, the use of corrosion inhibitors is essential for the

• Temporary protection of metals, whether during acid pickling and cleaning of installations or storage in the atmosphere (volatile inhibitors, incorporation into oils and greases for temporary protection) or for the treatment of cutting

• Paint industry on metals where the inhibitors are additives ensuring the

vided that the dry extract is greater than 92% of the mass paint.

paints on aluminum, as well as strontium chromate.

**28**

oils.

## **6. Green corrosion inhibitors (GCI)**

GCI is the molecule extract from plants; it has a double effect because it has a good ability to protect the metals and no negative effect on the environment at the same time.

In the last few years, the researcher community had oriented to inhibitors extracted from plants such as essential and vegetable oil, flavonoids, coumarins, steroids, terpenoids, and condensed tannins. These substances are excellent inhibitors because they contain heteroatoms such as an N, O, P, and S. The free electrons on the heteroatoms form bonds with the electrons on the metal surface. Some atoms in water ionize to release a proton; thus, the now negatively charged heteroatom helps to free an electron on the heteroatom and forms a stronger bond with the metallic electrons. These properties confer them good inhibition properties.

The following table summarized some green inhibitors used for corrosion inhibition of steels, steel alloys, aluminums, aluminum alloys, and other metals and alloys (**Table 1**).


#### **Table 1.**

*Green inhibitors used for corrosion inhibition of steel, steel alloys, aluminum, aluminum alloys, and other metals and alloys.*

#### **7. Green corrosion inhibitor study**

In this part, we will present a study of a green corrosion inhibitor using a formulation prepared based on the *Ceratonia siliqua* L. seed oil noted FCSL in simulated acid rain solution with pH equal to 3.6. This medium is simulated to acid rain in urban zone [26].

The inhibition effect was evaluated using the electrochemical measurement such as polarization curves and spectroscopy impedance. The electrode surface was characterized by SEM/EDS.

#### **7.1 Open circuit potential**

The results of the open circuit potential (OCP) variation of the iron substrate in acidic solution in the presence and in the absence of FCSL are reported in **Figure 6**.

The results show that in the absence of FCSL, the potential tends to stabilize at −0.51 V, after 20 min.

The addition of the FCSL formulation leads to a shift in the corrosion potential to a positive direction. This important shift of corrosion potential may indicate an important anodic inhibiting effect of FCSL.

#### **7.2 Potentiodynamic curves**

The polarization studies of iron were carried out in acid rain solution both in the absence and in the presence of the FCSL formulation.

All of these curves were obtained after 30 min of immersion time of the electrode in electrolytic solution after performing the automatic ohmic drop compensation (ZIR).

The cathodic and anodic polarization curves of iron in simulated acid rain solution with and without various inhibition concentrations are reported in **Figure 7**.

**Figure 6.**

*Variation of the open circuit potential (OCP) of the iron substrate in acidic solution with and without the FCSL formulation.*

**31**

range.

its value of 98.6%:

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

*7.2.1 The cathodic polarization*

expressed in the following equation:

dissolved oxygen toward the electrode surface.

reaction can be expressed by the following equation:

*E*(%) = *<sup>i</sup>*<sup>0</sup>

corrosion current density Icorr reduced from 74.9 mA cm<sup>−</sup><sup>2</sup>

*7.2.2 The anodic polarization*

the inhibitor to 1.0 mA cm<sup>−</sup><sup>2</sup>

transport [24].

**Figure 7.**

In absence of the inhibitor (**Figure 7a**), the corrosion current increases rapidly with the cathodic overvoltage until the potential value of −0.8 V/SCE; for more

*Potentiodynamic polarization curves of the iron in acid rain solution with and without various inhibition* 

In the cathodic process, the important factor that must be considered is the mass

The adding of the formulation to the corrosive solution is accompanied by both a

shift of corrosion potential Ecorr toward a more positive potential and a decrease of the current density Icorr, with the disappearance of the diffusion plateau,

obtained in the case of the blank solution, in the presence of the FCSL formulation. We observe the formation of the film on the area, which hinders the diffusion of

This behavior is associated with the presence of chloride in solution. The anodic

According to **Figure 7b** in the presence of the FCSL formulation, the current density decreases significantly with the presence of the inhibitor. Furthermore, the corrosion potential displayed more positive values, and also the value of the

times, then we observe the appearance of a current plateau in a wide potential

The inhibition efficiency (% IE) was calculated using the following relation and

*corr* − *i*0 \_ *Inh*

*i*0

2H2O + O2 + 4e<sup>−</sup> → 4OH<sup>−</sup> (1)

Fe → Fe2+ + 2e<sup>−</sup> (2)

in the presence of the inhibitor. So in less than 75

*corr* × 100 (3)

in the absence of

be attributed to the oxygen diffusion process, so the cathodic reaction can be

, which can

negative potential values, a pseudo-plateau appears in 0.4 mA/cm2

*concentrations in the cathodic domain (a) and in the anodic domain (b).*

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

**Figure 7.**

*Corrosion*

urban zone [26].

**Figure 6**.

tion (ZIR).

**Figure 7**.

characterized by SEM/EDS.

**7.1 Open circuit potential**

at −0.51 V, after 20 min.

**7.2 Potentiodynamic curves**

important anodic inhibiting effect of FCSL.

absence and in the presence of the FCSL formulation.

**7. Green corrosion inhibitor study**

In this part, we will present a study of a green corrosion inhibitor using a formulation prepared based on the *Ceratonia siliqua* L. seed oil noted FCSL in simulated acid rain solution with pH equal to 3.6. This medium is simulated to acid rain in

The inhibition effect was evaluated using the electrochemical measurement such as polarization curves and spectroscopy impedance. The electrode surface was

The results of the open circuit potential (OCP) variation of the iron substrate

The results show that in the absence of FCSL, the potential tends to stabilize

The addition of the FCSL formulation leads to a shift in the corrosion potential to a positive direction. This important shift of corrosion potential may indicate an

The polarization studies of iron were carried out in acid rain solution both in the

All of these curves were obtained after 30 min of immersion time of the electrode in electrolytic solution after performing the automatic ohmic drop compensa-

The cathodic and anodic polarization curves of iron in simulated acid rain solution with and without various inhibition concentrations are reported in

*Variation of the open circuit potential (OCP) of the iron substrate in acidic solution with and without the* 

in acidic solution in the presence and in the absence of FCSL are reported in

**30**

**Figure 6.**

*FCSL formulation.*

*Potentiodynamic polarization curves of the iron in acid rain solution with and without various inhibition concentrations in the cathodic domain (a) and in the anodic domain (b).*

#### *7.2.1 The cathodic polarization*

In absence of the inhibitor (**Figure 7a**), the corrosion current increases rapidly with the cathodic overvoltage until the potential value of −0.8 V/SCE; for more negative potential values, a pseudo-plateau appears in 0.4 mA/cm2 , which can be attributed to the oxygen diffusion process, so the cathodic reaction can be expressed in the following equation:

$$2\text{H}\_2\text{O} + \text{O}\_2 + 4\text{e}^- \rightarrow 4\text{OH}^- \tag{1}$$

In the cathodic process, the important factor that must be considered is the mass transport [24].

The adding of the formulation to the corrosive solution is accompanied by both a shift of corrosion potential Ecorr toward a more positive potential and a decrease of the current density Icorr, with the disappearance of the diffusion plateau, obtained in the case of the blank solution, in the presence of the FCSL formulation. We observe the formation of the film on the area, which hinders the diffusion of dissolved oxygen toward the electrode surface.

#### *7.2.2 The anodic polarization*

$$\text{Fe} \rightarrow \text{Fe}^{2+} + 2\text{e}^- \tag{2}$$

This behavior is associated with the presence of chloride in solution. The anodic reaction can be expressed by the following equation:

According to **Figure 7b** in the presence of the FCSL formulation, the current density decreases significantly with the presence of the inhibitor. Furthermore, the corrosion potential displayed more positive values, and also the value of the corrosion current density Icorr reduced from 74.9 mA cm<sup>−</sup><sup>2</sup> in the absence of the inhibitor to 1.0 mA cm<sup>−</sup><sup>2</sup> in the presence of the inhibitor. So in less than 75 times, then we observe the appearance of a current plateau in a wide potential range.

The inhibition efficiency (% IE) was calculated using the following relation and its value of 98.6%: *corr* − *i*0 \_

$$E\{\text{\textquotedblleft}\text{\textquotedblright}\} = \frac{i\_0^{\text{corr}} - i\_0^{\text{lab}}}{i\_0^{\text{corr}}} \times \mathbf{100} \tag{3}$$

The corresponding current plateau value is in the order of 0.03 mA cm<sup>−</sup><sup>2</sup> in the case of the FSCL formulation. This may indicate that the iron surface is protected by the inhibitor; this protection may be attributed to a passivity of iron substrate resulting from the formation of inhibitor film on the iron electrode surface. Thus results were observed by other authors [27].

From this result, we can conclude that the FSCL formulation is a mixed-type inhibitor that acts by decreasing the current density in both the cathodic and the anodic domains and making the corrosion potential become more anodic.

This good inhibiting effect of the FSCL formulation may be related to the adsorption on the electrode surface by the establishment of a barrier film.

#### **7.3 Electrochemical impedance spectroscopy**

The impedance diagrams in Nyquist and Bode plots in the absence and in the presence of the FCSL at 293 K are represented in **Figure 8**.

In the case of the blank solution, as shown in **Figure 8**, we noted the two capacity loops in the high frequencies and the inductive loop at low frequencies. This inductive effect may be due to the desorption of the H+ ions and salt ions present in the solution or to the redissolution of the passivity surface [26]. In effect, this inductive loop disappeared with the addition of the inhibitor. The same behavior has been observed by other authors [27].

As shown in **Figure 8**, in the presence of the FCSL formulation, the size of the loops are bigger than in the case of the blank. Indeed, the polarization resistances pass from 380 Ω cm2 in the case of blank to 14,080 Ω cm2 in the presence of inhibitor.

The inhibition efficiency (% IE) was calculated using the following relation and its value of 97.3%:

**Figure 8.** *Nyquist and Bode impedance plots of the iron electrode in acidic solution with and without the FCSL.*

**33**

**Figure 10.**

**Figure 9.**

*the absence of the FCSL formulation.*

*presence of the FCSL formulation.*

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

*E*(%) = *RP*

resistance (Rt) [10].

**7.4 Surface analysis**

marked the presence of oxygen atoms.

the presence of the ionized substances in the formulation.

*corr* − *RP* \_

*RP*

We noted also a decrease in the electrolyte resistance which may be explicated by

We can be ascribed to the following contributions. The high-frequency contribution (Cf, Rf) can be attributed to the dielectric character due to the formation of the film on the iron surface in presence of the inhibitor. The low-frequency contribution can be attributed to the double-layer capacitance (Cdl) at the electrolyte/iron interface at the bottom of the pores coupled with the charge transfer

The aim of the surface analysis by SEM coupled with the EDX used in this study is firstly to check the hypothesis of the formation of the inhibitor on the electrode surface and secondly to verify its protective qualities against iron corrosion.

**Figures 9** and **10** show the area of the substrate of iron with and without the

In the absence of the FSCL formulation (**Figure 9**), the SEM examination provides that the metallic surface be heavily attacked by the corrosive ions. The EDX spectrum reported in **Figure 9** showed the characteristic peaks of the specimen and

Also in the case of the presence the FSCL formulation (**Figure 10**), in the addition of the optimal concentration of the FSCL formulation into the corrosion

*SEM micrograph and EDS spectrum of the iron substrate in corrosive solution after 24 h of immersion time in* 

*SEM micrograph and EDX spectrum of the iron substrate in acidic solution after 24 h of immersion time in the* 

FCSL formulation after 24 h of immersion time in the acidic solution.

*Inh*

*corr* × 100 (4)

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

 *E*(%) = *RP corr* − *RP* \_ *Inh RP corr* × 100 (4)

We noted also a decrease in the electrolyte resistance which may be explicated by the presence of the ionized substances in the formulation.

We can be ascribed to the following contributions. The high-frequency contribution (Cf, Rf) can be attributed to the dielectric character due to the formation of the film on the iron surface in presence of the inhibitor. The low-frequency contribution can be attributed to the double-layer capacitance (Cdl) at the electrolyte/iron interface at the bottom of the pores coupled with the charge transfer resistance (Rt) [10].

#### **7.4 Surface analysis**

*Corrosion*

The corresponding current plateau value is in the order of 0.03 mA cm<sup>−</sup><sup>2</sup>

results were observed by other authors [27].

**7.3 Electrochemical impedance spectroscopy**

has been observed by other authors [27].

pass from 380 Ω cm2

its value of 97.3%:

inhibitor.

presence of the FCSL at 293 K are represented in **Figure 8**.

inductive effect may be due to the desorption of the H+

case of the FSCL formulation. This may indicate that the iron surface is protected by the inhibitor; this protection may be attributed to a passivity of iron substrate resulting from the formation of inhibitor film on the iron electrode surface. Thus

From this result, we can conclude that the FSCL formulation is a mixed-type inhibitor that acts by decreasing the current density in both the cathodic and the anodic domains and making the corrosion potential become more anodic. This good inhibiting effect of the FSCL formulation may be related to the adsorption on the electrode surface by the establishment of a barrier film.

The impedance diagrams in Nyquist and Bode plots in the absence and in the

In the case of the blank solution, as shown in **Figure 8**, we noted the two capacity loops in the high frequencies and the inductive loop at low frequencies. This

As shown in **Figure 8**, in the presence of the FCSL formulation, the size of the loops are bigger than in the case of the blank. Indeed, the polarization resistances

The inhibition efficiency (% IE) was calculated using the following relation and

in the solution or to the redissolution of the passivity surface [26]. In effect, this inductive loop disappeared with the addition of the inhibitor. The same behavior

in the case of blank to 14,080 Ω cm2

*Nyquist and Bode impedance plots of the iron electrode in acidic solution with and without the FCSL.*

in the

ions and salt ions present

in the presence of

**32**

**Figure 8.**

The aim of the surface analysis by SEM coupled with the EDX used in this study is firstly to check the hypothesis of the formation of the inhibitor on the electrode surface and secondly to verify its protective qualities against iron corrosion.

**Figures 9** and **10** show the area of the substrate of iron with and without the FCSL formulation after 24 h of immersion time in the acidic solution.

In the absence of the FSCL formulation (**Figure 9**), the SEM examination provides that the metallic surface be heavily attacked by the corrosive ions. The EDX spectrum reported in **Figure 9** showed the characteristic peaks of the specimen and marked the presence of oxygen atoms.

Also in the case of the presence the FSCL formulation (**Figure 10**), in the addition of the optimal concentration of the FSCL formulation into the corrosion

#### **Figure 9.**

*SEM micrograph and EDS spectrum of the iron substrate in corrosive solution after 24 h of immersion time in the absence of the FCSL formulation.*

#### **Figure 10.**

*SEM micrograph and EDX spectrum of the iron substrate in acidic solution after 24 h of immersion time in the presence of the FCSL formulation.*

solution, a smooth surface noted could explain the good protection effect of the inhibitor by a formation of the film. As confirmed by the EDX spectrum, a very low content of oxygen species is revealed.

### **8. Conclusion**

Corrosion is one of the most destructive phenomena that can affect metallic pieces. Through this work, we present one of the most used method to protect the metals: the corrosion inhibitor. In addition, we present a case study using a green corrosion inhibitor prepared from the oil of *Ceratonia siliqua* L. seeds.

### **Declaration of competing interest**

The authors have declared that no conflict of interest exists.

#### **Author details**

Said Abbout University Ibn Tofail, Kenitra, Morocco

\*Address all correspondence to: said.abbout@uit.ac.ma; said\_about@hotmail.fr

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**35**

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

Russian Agricultural Sciences.

[9] Palanisamy G. Corrosion Inhibitors. In: Corrosion Inhibitors. IntechOpen;

[10] Umoren SA, Solomon MM, Obot IB, Sulieman RK. A critical review on the recent studies on plant biomaterials as corrosion inhibitors for industrial metals. Journal of Industrial and Engineering Chemistry. 2019

[11] Henriquez-Román J, Sancy M, Páez M, Padilla-Campos L, Zagal J, Rangel C, et al. The influence of aniline and its derivatives on the corrosion behaviour of copper in acid solution. Journal of Solid State Electrochemistry.

[12] El Hosary A, Saleh R, El Din AS. Corrosion inhibition by naturally occurring substances—I. The effect of Hibiscus subdariffa (karkade) extract on the dissolution of Al and Zn. Corrosion Science. 1972;**12**:897-904

[13] Bouyanzer A, Majidi L, Hammouti B. Effect of eucalyptus oil on the corrosion of steel in 1M HCl. Bulletin of Electrochemistry.

[14] Chetouani A, Hammouti B. Corrosion inhibition of iron in

[15] Umoren S, Obot I, Ebenso E. Corrosion inhibition of aluminium using exudate gum from Pachylobus edulis in the presence of halide ions in HCl. Journal of Chemistry.

hydrochloric acid solutions by naturally henna. Bulletin of Electrochemistry.

[16] Okafor P, Osabor V, Ebenso E. Ecofriendly corrosion inhibitors: Inhibitive action of ethanol extracts of *Garcinia* 

2019;**45**:307-311

2005;**9**:504-511

2006;**22**:321-324

2003;**19**:23-25

2008;**5**:355-364

2019

[1] Yusoff MFM, Afiqah MI, Zulkafli Y, Othman NK, Lazim A, Mokhtar WNAW. Temperature effects toward corrosion rate of carbon and mild steel using red palm oil as natural corrosion inhibitor. Malaysian Journal of Chemistry (MJCHEM). 2019;**21**:64-70

[2] ISO 8044:2015 (en). Corrosion of metals and alloys—Basic terms and

[3] Zhang F, Chen C, Hou R, Li J, Cao Y,

Eslamimehr S, Lemieux MR, Ishizaki Y, Clemons WM Jr, et al. Semisynthesis of an anticancer DPAGT1 inhibitor from a muraymycin biosynthetic intermediate. Organic Letters. 2019;**21**:876-879

[5] Gangadhara G, Dahl G, Bohnacker T, Rae R, Gunnarsson J, Blaho S, et al. A class of highly selective inhibitors bind to an active state of PI3Kγ. Nature

Chemical Biology. 2019;**15**:348

[6] Tang Z. A review of corrosion inhibitors for rust preventative fluids. Current Opinion in Solid State and Materials Science. 2019;**23**:100759

[7] Frolenkova S, Overchenko T, Motronyuk T, Vorobyova V, Miroshnychenko I, Panchenko M. Passivating anions effect on the anodic behavior of steel in a converting acetate solution. Journal of Chemical

Technology and Metallurgy.

[8] Vigdorovich V, Tsygankova L, Knyazeva L. Universality of volatile corrosion inhibitors in terms of agricultural production requirements.

2019;**54**:443-446

Dong S, et al. Investigation and application of mussel adhesive protein nanocomposite film-forming inhibitor for reinforced concrete engineering. Corrosion Science. 2019;**153**:333-340

[4] Mitachi K, Kurosu SM,

definitions

**References**

*Green Inhibitors to Reduce the Corrosion Damage DOI: http://dx.doi.org/10.5772/intechopen.91481*

#### **References**

*Corrosion*

**8. Conclusion**

content of oxygen species is revealed.

**Declaration of competing interest**

solution, a smooth surface noted could explain the good protection effect of the inhibitor by a formation of the film. As confirmed by the EDX spectrum, a very low

Corrosion is one of the most destructive phenomena that can affect metallic pieces. Through this work, we present one of the most used method to protect the metals: the corrosion inhibitor. In addition, we present a case study using a green

corrosion inhibitor prepared from the oil of *Ceratonia siliqua* L. seeds.

The authors have declared that no conflict of interest exists.

**34**

**Author details**

University Ibn Tofail, Kenitra, Morocco

provided the original work is properly cited.

\*Address all correspondence to: said.abbout@uit.ac.ma; said\_about@hotmail.fr

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Said Abbout

[1] Yusoff MFM, Afiqah MI, Zulkafli Y, Othman NK, Lazim A, Mokhtar WNAW. Temperature effects toward corrosion rate of carbon and mild steel using red palm oil as natural corrosion inhibitor. Malaysian Journal of Chemistry (MJCHEM). 2019;**21**:64-70

[2] ISO 8044:2015 (en). Corrosion of metals and alloys—Basic terms and definitions

[3] Zhang F, Chen C, Hou R, Li J, Cao Y, Dong S, et al. Investigation and application of mussel adhesive protein nanocomposite film-forming inhibitor for reinforced concrete engineering. Corrosion Science. 2019;**153**:333-340

[4] Mitachi K, Kurosu SM, Eslamimehr S, Lemieux MR, Ishizaki Y, Clemons WM Jr, et al. Semisynthesis of an anticancer DPAGT1 inhibitor from a muraymycin biosynthetic intermediate. Organic Letters. 2019;**21**:876-879

[5] Gangadhara G, Dahl G, Bohnacker T, Rae R, Gunnarsson J, Blaho S, et al. A class of highly selective inhibitors bind to an active state of PI3Kγ. Nature Chemical Biology. 2019;**15**:348

[6] Tang Z. A review of corrosion inhibitors for rust preventative fluids. Current Opinion in Solid State and Materials Science. 2019;**23**:100759

[7] Frolenkova S, Overchenko T, Motronyuk T, Vorobyova V, Miroshnychenko I, Panchenko M. Passivating anions effect on the anodic behavior of steel in a converting acetate solution. Journal of Chemical Technology and Metallurgy. 2019;**54**:443-446

[8] Vigdorovich V, Tsygankova L, Knyazeva L. Universality of volatile corrosion inhibitors in terms of agricultural production requirements. Russian Agricultural Sciences. 2019;**45**:307-311

[9] Palanisamy G. Corrosion Inhibitors. In: Corrosion Inhibitors. IntechOpen; 2019

[10] Umoren SA, Solomon MM, Obot IB, Sulieman RK. A critical review on the recent studies on plant biomaterials as corrosion inhibitors for industrial metals. Journal of Industrial and Engineering Chemistry. 2019

[11] Henriquez-Román J, Sancy M, Páez M, Padilla-Campos L, Zagal J, Rangel C, et al. The influence of aniline and its derivatives on the corrosion behaviour of copper in acid solution. Journal of Solid State Electrochemistry. 2005;**9**:504-511

[12] El Hosary A, Saleh R, El Din AS. Corrosion inhibition by naturally occurring substances—I. The effect of Hibiscus subdariffa (karkade) extract on the dissolution of Al and Zn. Corrosion Science. 1972;**12**:897-904

[13] Bouyanzer A, Majidi L, Hammouti B. Effect of eucalyptus oil on the corrosion of steel in 1M HCl. Bulletin of Electrochemistry. 2006;**22**:321-324

[14] Chetouani A, Hammouti B. Corrosion inhibition of iron in hydrochloric acid solutions by naturally henna. Bulletin of Electrochemistry. 2003;**19**:23-25

[15] Umoren S, Obot I, Ebenso E. Corrosion inhibition of aluminium using exudate gum from Pachylobus edulis in the presence of halide ions in HCl. Journal of Chemistry. 2008;**5**:355-364

[16] Okafor P, Osabor V, Ebenso E. Ecofriendly corrosion inhibitors: Inhibitive action of ethanol extracts of *Garcinia* 

*kola* for the corrosion of mild steel in H2SO4 solutions. Pigment & Resin Technology. 2007;**36**:299-305

[17] Ramachandra C, Rao PS. Processing of Aloe vera leaf gel: A review. American Journal of Agricultural and Biological Sciences. 2008;**3**:502-510

[18] Ezugwu A, Ezike T, Ibeawuchi A, Nsude C, Udenwobele D, Eze S, et al. Comparative studies on pectinases obtained from *Aspergillus fumigatus* and *Aspergillus niger* in submerged fermentation system using pectin extracted from mango, orange and pineapple peels as carbon sources. Nigerian Journal of Biotechnology. 2014;**28**:26-34

[19] Oguzie EE. Corrosion inhibitive effect and adsorption behaviour of *Hibiscus sabdariffa* extract on mild steel in acidic media. Portugaliae Electrochimica Acta. 2008;**26**:303-314

[20] Kliškić M, Radošević J, Gudić S, Katalinić V. Aqueous extract of *Rosmarinus officinalis* L. as inhibitor of Al–Mg alloy corrosion in chloride solution. Journal of Applied Electrochemistry. 2000;**30**:823-830

[21] El-Etre A. Inhibition of aluminum corrosion using Opuntia extract. Corrosion Science. 2003;**45**:2485-2495

[22] Müller B. Amino and polyamino acids as corrosion inhibitors for aluminium and zinc pigments. Pigment & Resin Technology. 2002;**31**:84-87

[23] El-Etre A. Natural onion juice as inhibitor for zinc corrosion. Bulletin of Electrochemistry. 2006;**22**:75-80

[24] Vrsalović L, Gudić S, Kliškić M. *Salvia officinalis* L. honey as corrosion inhibitor for CuNiFe alloy in sodium chloride solution. Indian Journal of Chemical Technology. 2012;**19**(2): 96-102

[25] Left DB, Zertoubi M, Irhzo A, Azzi M. Revue: Huiles et Extraits de plantes comme inhibiteurs de corrosion pour différents métaux et alliages dans le milieu acide chlorhydrique. [Review: Oils and extracts plants as corrosion inhibitors for different metals and alloys in hydrochloric acid medium]. Journal of Materials and Environmental Science. 2013;**4**(6):855-866

[26] Abbout S, Chellouli M, Zouarhi M, Benzidia B, Hammouch H, Chebabe D, et al. New formulation based on *Ceratonia siliqua* L seed oil, as a green corrosion inhibitor of iron in acidic medium. Analytical & Bioanalytical Electrochemistry. 2018;**10**:789-804

[27] Zouarhi M, Chellouli M, Abbout S, Hammouch H, Dermaj A, Said Hassane SO, et al. Inhibiting effect of a green corrosion inhibitor containing *Jatropha curcas* seeds oil for iron in an acidic medium. Portugaliae Electrochimica Acta. 2018;**36**:179-195

**37**

out inhibitors.

**Chapter 3**

*Anil Kumar*

**Abstract**

efficacy.

**1. Introduction**

Introduction of Inhibitors,

Corrosion in Concrete

Mechanism and Application for

Protection of Steel Reinforcement

The corrosion of steel reinforcement in concrete due to environmental factors has been studied through numerous approaches and the reduction of corrosion has been managed by various methods; however, among the protection techniques, the use of corrosion inhibitors has gained encouragement. In this chapter, nitrites and nitrates of sodium and calcium and sodium molybdates and sodium tungstates (oxyanions of group VI) were studied and have gained sufficient scientific coverage. However, their exact role of inhibition was studied by simple polarization technique. In this chapter, we compare the inhibitive efficiency of nitrites and nitrates of sodium and calcium and also that of molybdates and tungstates. The results, however, indicate that among nitrites and nitrates, the calcium salts are more efficient and molybdates and tungstates are comparable in their inhibitive

**Keywords:** corrosion, steel reinforcement, inhibitors, polarization, mechanism, Icorr

Corrosion is the destructive attack upon a metal by its environment and it is an electrochemical phenomenon. Most common examples of corrosion include the rusting of iron and steel, tarnishing of silver and copper, blistering and bubbling of chromium plating and paintwork on cars, discharge of rustcoloured water from domestic taps and seizure of nuts and bolts. Corrosion leads to weakening of metal structures, failure of plant and pollution of process liquors. It is necessary to understand the basic principles of corrosion before taking appropriate preventative or protective measures. The various efforts towards reducing corrosion of metals can be grouped into the following: modification of bulk alloys, modification of environments and surface modifications. Here, in this chapter, we discuss the modification of environments by adding small concentration of inhibitors. An inhibitor is a chemical substance that inhibits or effectively decreases the corrosion rate. It can be understand by **Figure 1**, Icorr. decreases with inhibitors in comparison to with-

#### **Chapter 3**

*Corrosion*

*kola* for the corrosion of mild steel in H2SO4 solutions. Pigment & Resin

[17] Ramachandra C, Rao PS. Processing of Aloe vera leaf gel: A review. American Journal of Agricultural and Biological

[25] Left DB, Zertoubi M, Irhzo A, Azzi M. Revue: Huiles et Extraits de plantes comme inhibiteurs de corrosion pour différents métaux et alliages dans le milieu acide chlorhydrique. [Review: Oils and extracts plants as corrosion inhibitors for different metals and alloys in hydrochloric acid medium]. Journal of Materials and Environmental

Science. 2013;**4**(6):855-866

[26] Abbout S, Chellouli M, Zouarhi M, Benzidia B, Hammouch H, Chebabe D, et al. New formulation based on *Ceratonia siliqua* L seed oil, as a green corrosion inhibitor of iron in acidic medium. Analytical & Bioanalytical Electrochemistry. 2018;**10**:789-804

[27] Zouarhi M, Chellouli M, Abbout S,

Hammouch H, Dermaj A, Said Hassane SO, et al. Inhibiting effect of a green corrosion inhibitor containing *Jatropha curcas* seeds oil for iron in an acidic medium. Portugaliae Electrochimica Acta. 2018;**36**:179-195

[18] Ezugwu A, Ezike T, Ibeawuchi A, Nsude C, Udenwobele D, Eze S, et al. Comparative studies on pectinases obtained from *Aspergillus fumigatus* and *Aspergillus niger* in submerged fermentation system using pectin extracted from mango, orange and pineapple peels as carbon sources. Nigerian Journal of Biotechnology.

[19] Oguzie EE. Corrosion inhibitive effect and adsorption behaviour of *Hibiscus sabdariffa* extract on mild steel in acidic media. Portugaliae Electrochimica Acta. 2008;**26**:303-314

[20] Kliškić M, Radošević J, Gudić S, Katalinić V. Aqueous extract of *Rosmarinus officinalis* L. as inhibitor of Al–Mg alloy corrosion in chloride

[21] El-Etre A. Inhibition of aluminum corrosion using Opuntia extract. Corrosion Science. 2003;**45**:2485-2495

[22] Müller B. Amino and polyamino acids as corrosion inhibitors for

[23] El-Etre A. Natural onion juice as inhibitor for zinc corrosion. Bulletin of Electrochemistry. 2006;**22**:75-80

[24] Vrsalović L, Gudić S, Kliškić M. *Salvia officinalis* L. honey as corrosion inhibitor for CuNiFe alloy in sodium chloride solution. Indian Journal of Chemical Technology. 2012;**19**(2):

aluminium and zinc pigments. Pigment & Resin Technology. 2002;**31**:84-87

solution. Journal of Applied Electrochemistry. 2000;**30**:823-830

Technology. 2007;**36**:299-305

Sciences. 2008;**3**:502-510

2014;**28**:26-34

**36**

96-102
